For his science project, Austin wants to determine if the pH of standing rainwater changes over time. He collects rainwater and distributes it evenly in 5 jars and places them all indoors in a spot that does not receive a lot of sunlight to limit evaporation. Using a pH testing kit, he measures the pH of the water in the first jar on the 4th day, second jar on the 8th day, third jar on the 12th day, fourth jar on the 16th day and fifth jar on the 20th day. What is the independent, or manipulated, variable in Austin's experiment?

This question lacks options, the options are:

A. the number of days the rainwater was allowed to sit

B. the number of times the rainwater was observed

C. the change in the amount of rainwater due to evaporation

D. the change in pH of the rainwater over time

The answer is A

Explanation:

In an experiment, the independent variable is the variable that is changed or manipulated by the experimenter in order to effect a measurable response.

In this experiment, Austin is trying to determine how time changes the pH of standing rainwater. He collects rainwater and distributes it evenly in 5 jars, which he measured the pH at different days using a pH testing kit. Hence, the independent or manipulated variable is THE NUMBER OF DAYS THE RAINWATER WAS ALLOWED TO SIT before measuring their pH.

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.

it is the second option.